The present invention relates to methods for fabricating a semiconductor device, and more particularly relates to a method for forming an interconnect of a semiconductor device.
In recent years, copper has been commonly used as an interconnect material for semiconductor devices. In process steps for processing an interconnect formed by using copper as an interconnect material, used is a damascene process in which an interconnect groove is formed by a dry etching technique and then an interconnect material is filled into the interconnect groove (see, e.g., Japanese Unexamined Patent Publication No. 2001-196371).
Hereinafter, a method for forming an interconnect in a known semiconductor device will be described with reference to the accompanying drawings.
FIGS. 8A through 8D are cross-sectional views illustrating respective process steps for fabricating a known semiconductor device.
First, as shown in FIG. 8A, a silicon oxide film 102 is formed on a semiconductor substrate 101 of silicon and then an interconnect groove is formed in the silicon oxide film 102. Next, a conductive pattern 103 of copper is formed so as to be filled in the interconnect groove formed in the silicon oxide film 102. Subsequently, an insulating film 104 is formed on the silicon oxide film 102 and the conductive pattern 103, and then a resist pattern 105 having an opening 105a is formed on the insulating film 104.
Next, as shown in FIG. 8B, the insulating film 104 is etched by plasma dry etching using the resist pattern 105 as a mask to form an opening 104a in the insulating film 104. In this manner, the surface of the conductive pattern 103 is exposed. The plasma dry etching is performed using a parallel plate RIE system under the conditions where the flow rate of a CF4 gas as an etching gas is 50 mL/min (normal state), the flow rate of an O2 gas as a control gas for a deposit to be etched is 10 mL/min (normal state), the substrate temperature is 25xc2x0 C., the RF output power is 1000 W, and the inside chamber pressure is 5 Pa.
Next, as shown in FIG. 8C ashing using an oxygen gas is performed to remove the resist pattern 105. The ashing is performed using a microwave plasma ashing system under the conditions where the flow rate of an oxygen gas is 1000 mL/min (normal state), the microwave output power is 2000 W, the discharge time is about 1 minute, the substrate temperature is about 250xc2x0 C. and the pressure is about 100 Pa. By the ashing, a copper oxide layer 103a having a thickness of about 40 nm is formed on the surface of the conductive film 103.
Next, as shown in FIG. 8D, the copper oxide layer 103a which has been formed during the ashing is removed by cleaning using an organic acid cleaning agent containing aluminum fluoride, and Ar sputtering. Thereafter, a conductive film 106 is formed on part of the conductive pattern 103 from which the copper oxide layer 103a has been removed and the insulating film 104.
In the method for fabricating a known semiconductor device, however, the thickness of the copper oxide layer 103a formed on the surface of the conductive pattern 103 is about 40 nm. That is to say, the copper oxide layer 103a is relatively thick. Accordingly, the copper oxide layer 103a can not be entirely removed by an organic acid cleaning and Ar sputtering, and thus the copper oxide layer 103a is left between the conductive pattern 103 and the conductive film 106, as shown in FIG. 8D. This results in an increase in contact resistance between the conductive pattern 103 and the conductive film 106 or variations in contact resistance therebetween the conductive pattern 103 and the conductive film 106.
The present invention aims to prevent the progress of oxidation of a conductive pattern in removing a resist pattern and also to prevent the formation of a thick oxide film which is difficult to be removed on the surface of the conductive pattern.
To solve the above-described problems, a first method for fabricating a semiconductor device according to the present invention is characterized by comprising the steps of: forming an insulating film on a conductive pattern formed on a substrate; forming a resist pattern on the insulating film; performing etching to the insulating film using the resist pattern as a mask to form in the insulating film an opening at which part of the surface of the conductive pattern is exposed; forming an antioxidant layer on the part of surface of the conductive pattern exposed while removing the resist pattern; and depositing a conductive film on the conductive pattern from which the antioxidant layer has been removed.
In the first method for fabricating a semiconductor device, an antioxidant layer for preventing oxidation of an conductive pattern is formed on the surface of the conductive pattern while a resist pattern is removed. Thus, it is possible to prevent the progress of oxidation of the conductive pattern in removing the resist pattern and also to prevent the formation of a thick oxide film which is difficult to be removed. Moreover, the antioxidant layer formed on the surface of the conductive pattern can be removed in a simple manner, and thus it is possible to prevent an oxide film from being interposed between the conductive pattern and the conductive film. Therefore, the contact resistance between the conductive pattern and the conductive film can be reduced and variations in the contact resistance therebetween can be suppressed.
In the first method for fabricating a semiconductor device, it is preferable that the conductive pattern contains Cu and the antioxidant layer contains CuO as a main component.
Thus, since an antioxidant layer containing CuO is passive, it prevents oxidation of part of a conductive pattern located under the antioxidant layer. Therefore, it is possible to prevent the formation of a thick oxide film which is difficult to be removed. Accordingly, the antioxidant layer formed on the surface of the conductive layer can be removed in a simple manner.
In the first method for fabricating a semiconductor device, it is preferable that the step of forming an antioxidant layer includes performing oxygen plasma treatment with a substrate temperature of 120xc2x0 C. or less.
Thus, the proportion of CuO in an antioxidant layer formed on the surface of the conductive pattern is increased while the proportion of Cu2O therein is reduced. Accordingly, oxidation of the conductive pattern located under the antioxidant layer can be further suppressed and thus the formation of a thick oxide film which is difficult to be removed on the surface of the conductive pattern can be reliably prevented. Therefore, the antioxidant layer formed on the surface of the conductive pattern can be removed in a more simple manner.
In the first method for fabricating a semiconductor device, it is preferable that the step of forming an antioxidant layer includes performing oxygen plasma treatment with a chamber pressure of 40 Pa or less.
Thus, the proportion of CuO in an antioxidant layer formed on the surface of the conductive pattern is increased while the proportion of Cu2O therein is reduced. Accordingly, oxidation of the conductive pattern located under the antioxidant layer can be further suppressed and thus the formation of a thick oxide film which is difficult to be removed on the surface of the conductive pattern can be reliably prevented. Therefore, the antioxidant layer formed on the surface of the conductive pattern can be removed in a more simple manner.
A second method for fabricating a semiconductor device according to the present invention is characterized by comprising the steps of: forming an insulating film on a conductive pattern formed on a substrate; forming a resist pattern on the insulating film; performing etching to the insulating film using the resist pattern as a mask to form in the insulating film an opening at which part of the surface of the conductive pattern is exposed; forming an antioxidant layer on the part of the surface of the conductive pattern exposed; removing the resist pattern; and depositing a conductive film on the conductive pattern from which the antioxidant layer has been removed.
In the second method for fabricating a semiconductor device, an antioxidant layer is formed on the surface of a conductive pattern and then a resist pattern is removed. Thus, it is possible to prevent the progress of oxidation of the conductive pattern in removing the resist pattern and also to prevent the formation of a thick oxide film which is difficult to be removed. Moreover, the antioxidant layer formed on the surface of the conductive pattern can be removed in a simple manner, and thus it is possible to prevent an oxide film from being interposed between the conductive pattern and the conductive film. Therefore, the contact resistance between the conductive pattern and the conductive film can be reduced and variations in the contact resistance therebetween can be suppressed. Furthermore, the antioxidant layer has been formed on the surface of the conductive pattern before removing the resist pattern. Thus, the resist pattern can be removed in a short time.
In the second method for fabricating a semiconductor device, it is preferable that the conductive pattern contains Cu and the antioxidant layer contains CuO as a main component.
Thus, since an antioxidant layer containing CuO is passive, it prevents oxidation of part of a conductive pattern located under the antioxidant layer. Therefore, it is possible to prevent the formation of a thick oxide film which is difficult to be removed. Accordingly, the antioxidant layer formed on the surface of the conductive layer can be removed in a simple manner.
In the second method for fabricating a semiconductor device, it is preferable that the step of removing the resist pattern includes performing oxygen plasma treatment with a substrate temperature of not less than 200xc2x0 C. and not more than 250xc2x0 C.
Thus, a resist pattern can be removed in a short time.
In the second method for fabricating a semiconductor device, it is preferable that the step of forming an antioxidant layer includes performing oxygen plasma treatment with a first substrate temperature, and the step of removing the resist pattern includes performing oxygen plasma treatment with a second substrate temperature which is higher than the first substrate temperature.
Thus, it is possible to prevent the formation of a thick oxide film which is difficult to be removed and also to remove a resist pattern in a short time.
In the second method for fabricating a semiconductor device, it is preferable that the step of forming an antioxidant layer includes performing oxygen plasma treatment at a first pressure, and the step of removing the resist pattern includes performing oxygen plasma treatment at a second pressure which is higher than the first pressure.
Thus, it is possible to prevent the formation of a thick oxide film which is difficult to be removed and also to remove a resist pattern in a short time.
In the second method for fabricating a semiconductor device, the step of forming an antioxidant layer includes performing reactive ion treatment to the conductive pattern, and the step of forming a resist pattern includes performing oxygen plasma treatment.
Thus, it is possible to form an antioxidant layer and remove a resist pattern in a single chamber. Accordingly, an opening at which a conductive pattern is exposed is not exposed to the air, and therefore the progress of oxidation of the surface of the conductive pattern can be prevented.